Jaewoo Noh

Pure-state single-photon wave-packet generation by parametric down-conversion in a distributed microcavity

We propose an optical parametric down-conversion (PDC) scheme that does not suffer a trade-off between the state purity of single-photon wave packets and the rate of packet production. This is accomplished by modifying the PDC process by using a microcavity to engineer the density of states of the optical field at the PDC frequencies. The high-finesse cavity mode occupies a spectral interval much narrower than the bandwidth of the pulsed pump laser field, suppressing the spectral correlation, or entanglement, between signal and idler photons. Spectral filtering of the field occurs prior to photon creation rather than afterward as in most other schemes. Operator-Maxwell equations are solved to find the Schmidt-mode decomposition of the two-photon states produced. Greater than 99% pure-state packet production is predicted to be achievable.

Remote preparation of complex spatial states of single photons and verification by two-photon coincidence experiment

We propose and provide experimental evidence in support of a theory for the remote preparation of a complex spatial state of a single photon. An entangled two-photon source was obtained by spontaneous parametric down-conversion, and a double slit was placed in the path of the signal photon as a scattering object. The signal photon was detected after proper spatial filtering so that the idler photon was prepared in the corresponding single-photon state. By using a two-photon coincidence measurement, we obtained the Radon transform, at several longitudinal distances, of the single-photon Wigner distribution function modified by the double slit. The experimental results are consistent with the idler photon being in a pure state. An inverse Radon transformation can, in principle, be applied to the measured data to reconstruct the modified single-photon Wigner function, which is a complete representation of the amplitude and phase structure of the scattering object.

Transferring the spatial state of an entangled photon pair to a single photon by photon detection

We show theoretically that the spatial state of entangled photons generated by parametric down-conversion can be transferred to the spatial state of an idler photon by signal photon detection. This study considered the general condition with an arbitrary pump field profile and the detection of a signal photon at an arbitrary distance from a nonlinear crystal where the entangled photons are generated. Upon the detection of a signal photon, the two-photon state function of the entangled state can be transferred to a single-photon state function of the idler field due to the EPR type correlation between the signal and idler fields. The spatial state of the idler field contains more information on the original two-photon state.

Measurement of Spatial Coherence Function of Laser Beam by using a Sagnac Interferometer

The spatial coherence function of a laser beam was measured by using a Sagnac interferometer and self referencing technique. For a laser beam passing through a narrow slit, the absolute value of the measured spatial coherence function becomes more symmetric as the slit size is reduced. For diverging beams, the spatial coherence function shows fast oscillations in its real and imaginary parts. We explain this by using a Gaussian Schell-model. One can use this measurement method to study and characterize the property of the light field coming out of a small sample.

Measurement of Coherence and Beam Parameter of a Propagating Laser Beam by using Wigner Distribution Function Measurement

The spatial coherence and propagation property of a laser beam propagating through several optical components were studied experimentally by using the Wigner distribution function measurement method. It is shown experimentally that the total degree of coherence, the beam quality parameter, and the near and the far field information of the propagating beam can be obtained from the Wigner function measurement at one plane. More complete characterization of the laser beam was achieved by applying Schmidt mode decomposition to the Wigner distribution function, spatial coherence function, and directional coherence function, respectively. Fine details of the coherence property can be understood by the characteristics of the contributing eigenmodes.

Weak Value Measurement of an Optical Beam Deflection in Image Rotating Sagnac Interferometer

We measured small optical beam deflection in an image rotating Sagnac interferometer. We used a weak value measurement scheme that involves a pre-selection, weak perturbation, and a post-selection procedure to obtain the amplified value of beam deflection. The amplification factor of the measured beam deflection varied from 11 to 63 depending on the settings of the post-selection polarizer in front of the photodetector and the settings of polarization compensator in the interferometer.

Relative Particle Nature and Nonclassicality of Light

Theory on the creation of exactly n photon added pure quantum state is presented and its nonclassical property is studied.

An experiment on the stimulated emission of the evanescent photon

We studied experimentally the amplification of light beam reflected from a plane boundary, where a gain medium is placed in the transmitted beam region. It is shown that the reflected light beam is amplified due to the stimulated emission of photons from the dye molecules coupled to the evanescent wave. The experimental result is compared with the quantum theory developed recently, and the meaning of photon is reexamined.